Bug 47351 - Improper kerning of subscripts for italic characters
Summary: Improper kerning of subscripts for italic characters
Status: NEW
Alias: None
Product: LibreOffice
Classification: Unclassified
Component: Writer (show other bugs)
(earliest affected)
Inherited From OOo
Hardware: All All
: medium minor
Assignee: Not Assigned
: 91021 (view as bug list)
Depends on:
Blocks: Font-Rendering
  Show dependency treegraph
Reported: 2012-03-15 05:26 UTC by bellgardt
Modified: 2022-11-29 02:18 UTC (History)
3 users (show)

See Also:
Crash report or crash signature:

Document demonstrating the inappropriate kerning (22.00 KB, application/vnd.oasis.opendocument.text)
2012-03-15 05:26 UTC, bellgardt
File showing the problem still present on LO 7.2.2 (38.92 KB, application/vnd.oasis.opendocument.text)
2021-11-12 18:44 UTC, Rafael Lima
Fake-sups-vs-real-sups (47.78 KB, image/png)
2022-11-29 02:16 UTC, LibreTraining

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Description bellgardt 2012-03-15 05:26:54 UTC
Created attachment 58504 [details]
Document demonstrating the inappropriate kerning

When subscripts or superscripts are applied to italic text the optical impression is different for both types. The spacing behind a normal letter and a following subscript is much bigger compared to a superscript. The attached document demonstrates this effect and shows how it should look, e.g. in MS Word.

This problem existed already in OOo and is still present in LO
Comment 1 sasha.libreoffice 2012-06-08 00:53:17 UTC
Thanks for bugreport
reproduced in 3.3.4 and 3.5.4 on Fedora 64 bit using attachment
reproduced in 3.5.4 on Windows XP with TimesNewRoman, typed manually
Problem presents also in Calc and Impress

Retaining version to [unspecified], because bug inherited from OOo

PS: I do not know, which version is more correct, Word or Writer. But more short distance (Word) looks more beautiful. 
Another potential problem: incorrect opening documents from msOffce, because text will not fit in specified area on page due to bigger distance between characters.
Comment 2 QA Administrators 2015-01-05 17:52:11 UTC Comment hidden (obsolete)
Comment 3 bellgardt 2015-01-06 14:18:49 UTC
The bug still exists in LO (Build ID: e183d5b). Tested with 32-bit version on Windows 7 64 bit.
Comment 4 bellgardt 2015-01-06 14:21:27 UTC
Bug also present in LO, Build-ID: 3a87456aaa6a95c63eea1c1b3201acedf0751bd5
on same system as before.
Comment 5 Buovjaga 2015-05-05 14:14:42 UTC
*** Bug 91021 has been marked as a duplicate of this bug. ***
Comment 6 QA Administrators 2016-09-20 09:37:18 UTC Comment hidden (obsolete)
Comment 7 bellgardt 2016-10-04 14:22:32 UTC
Bug still exists in Version:
Build-ID: 8f96e87c890bf8fa77463cd4b640a2312823f3ad
Comment 8 bellgardt 2017-11-10 13:23:20 UTC
Bug still exists in version:
Build-ID: 92a7159f7e4af62137622921e809f8546db437e5
CPU-Threads: 4; System: Windows 6.1; UI-Render: Standard; 
Gebietsschema: de-DE (de_DE); Calc: CL
Comment 9 QA Administrators 2019-10-22 02:32:00 UTC Comment hidden (obsolete)
Comment 10 Rafael Lima 2021-11-12 18:44:33 UTC
Created attachment 176217 [details]
File showing the problem still present on LO 7.2.2

This bug persists in LO 7.2.2. I attached an updated image showing the current situation, which actually did not change.

Basically the kerning is incorrect using Liberation Serif in italic mode, both in Writer and in Math.

System info:
Version: / LibreOffice Community
Build ID: 20(Build:2)
CPU threads: 16; OS: Linux 5.13; UI render: default; VCL: kf5 (cairo+xcb)
Locale: pt-BR (pt_BR.UTF-8); UI: en-US
Ubuntu package version: 1:7.2.2-0ubuntu0.21.10.1
Calc: threaded
Comment 11 ⁨خالد حسني⁩ 2022-11-20 19:21:48 UTC
Do we have any example of other (office) software that handles this differently? It is not an issue of kerning, rather italic glyphs because of their slant will have more white space at the bottom than at the top.

LibreOffice is positioning the scripts using the glyph advance width, which does not compensate for the slant. One way to fix this is to use the glyph bounding rectangle, but this can be very tricky and slow.
Comment 12 LibreTraining 2022-11-29 02:16:12 UTC
Created attachment 183877 [details]
Comment 13 LibreTraining 2022-11-29 02:18:18 UTC
The created italic superscript and subscript characters should shift up or down along the italic angle.
Right now they are going straight up or down.

Attached is a comparison of the faked Liberation Serif superscript and the real Calibri superscript.
Note how the faked Liberation Serif superscript moves straight up and collides with the H. 
It should move up and to the right along the italic angle.

With Calibri you can see how the superscript K moves up and right.
Actually it is just like the top half of any italic character, which going to be shifted in the box.

And the subscript looks to far away as it should shift to the left.

See screenshot: